1. Field of the Invention
The present invention relates to an improved system for transmitting a scramble signal for a sky port scramble system.
2. Description of the Prior art
In recent years, it has been proposed to provide such a sky port scramble system that toll information such as a video signal, an audio signal or the like is provided to particular receiving contractors by using a communication satellite or a broadcasting satellite. In the scramble system such as the sky port scramble system, in order to keep an audio signal or a video signal to be transmitted in electrically secret, a signal switching system within the scanning line or a scanning line transfer system etc. is applied to a video signal etc. and also a pseudo random signal additive system etc. are applied to an audio signal etc.
Also, it has been proposed to provide such a business television system or the like that various kinds of video, audio and digital data or the like are transmitted between enterprises by using the scramble system so as to keep the data in secret. An example of this conventional business television system is shown in FIG. 1.
In FIG. 1, video or audio data or the like to be transmitted is supplied from a data source 19 to an active unit 21 constituting a first control system through a movable contact a and a stationary contact b of a switch 20. The first control system 21 includes a controller 23 and a scrambler 25. The data applied to the first control system 21 from the data source 19 is subjected to a predetermined scramble and then delivered as an output signal to a transmitter etc. through a switcher 27 to thereby be broadcast in accordance with a predetermined transmission system.
A standby unit 22 constituting a second control system and connected to another stationary contact c of the switch 20 includes a controller 24 and a scrambler 26 which have the same constructions as those of the controller 23 and the scrambler 25 of the active unit 21, respectively. The output signal from the second control unit 23 is applied to the switcher 27.
In this conventional system, if a fault occurs in the active unit 21 or the first control system, by changing over the movable contact a of the switch 20 to the stationary contact c to which the standby unit or the second control unit 22 is connected, the output data from the data source 19 can be transmitted.
In the conventional business television system of FIG. 1, however, in order to make the data state of the standby unit 22 concident with the current data state of the active unit 21 in a faulty state, it is insufficient to merely change over the switch 20 because the current data of the active unit 21 stored in a floppy disk etc. thereof have to be transmitted to the standby unit 22 and to make its data state concident with that of the active unit 21. Namely, it requires complicated procedures and takes much time to make the data state of the standby unit 22 coincide with the current data state of the faulty active unit 21.
This business television system may be applied to the sky port scramble system. However, in case of allotting addresses independently to respective customers who receive the data in this sky port scramble system, the number of the addresses in the business television system will be several thousands, while the number of the addresses in the sky port scramble system will be 25 millions at maximum. Thus, in the system where the business television system is applied to the sky port scramble system, it takes quite much time to make the data state of the standby unit 22 coincide with the current data state of the faulty active unit 21. Further, even if a fault or an obstacle occurs at independently authorized receivers etc., e.g. particular ones among 25 million receivers etc., many viewers or receiving contractors are affected by the fault.